Field of Invention
The present invention relates to a field of laser technology, and more particularly to a spatiotemporally resolved far-field pulse contrast measuring method and a device thereof, and an online identification method for origins of spatiotemporal noise.
Description of Related Arts
Pulse contrast is an important parameter of ultrahigh-peak-power lasers, defined as the intensity ratio of the pulse peak to its background noise. If the contrast of a laser pulse is not high enough, the background noise will disturb the interaction between the main pulse and the experimental target. Therefore, to control and measure the pulse contrast is advantageous to the smooth implement of laser-matter interacting experiments.
The measurement of the pulse contrast is mainly based on the optical cross-correlation technology. An under-test pulse and a sampling pulse which has a higher contrast than the under-test pulse make a cross-correlation in a nonlinear crystal, in such a manner that the contrast of the under-test pulse is obtained by detecting the relationship between the correlating signal intensity and the time delay of the two pulses. The time-scanning third-order cross-correlator has been commercialized (Sequoia, Amplitude Technologies, France), wherein a sampling pulse generated by a frequency multiplier makes a sum-frequency-generation-based interaction with an under-test pulse in a crystal, generating a third-harmonic signal detected by a photomultiplier. To measure the pulse contrast of the laser systems with a low repetitive rate, the single-shot cross-correlator has also been developed, which mainly depends on the non-collinear interaction between the under-test pulse and the sampling pulse for converting the temporal intensity information of the under-test pulse into the spatial intensity information of the correlating signal.
The conventionally available scanning or single-shot cross-correlation technologies are merely performed in the temporal domain and commonly in the near-field. However, the physical experiments are generally made at the focus (i.e., the far-field) of the driving laser. The latest studies demonstrated that some laser noises would exhibit a spatiotemporal-coupling characterization in a far-field, resulting in a space-dependent pulse contrast in essence. In this condition, the measurement for the pulse contrast must be performed in both the temporal domain and the spatial domain in the far-field of the laser beam. Unfortunately, the conventional temporal cross-correlation technologies have no such capability.